2.3. Micro coulometric titration system and procedure
A liquid drop can behave as a micro coulometric cell (“coulometric
drop cell”). The electrode system is composed of a working
electrode (WE) made of platinum wire (0.5 mm diameter) or
stainless steel and an auxiliary electrode (AE) fabricated from a
disposable glass dropper. The auxiliary electrode contained 2%
agar in 3 M KCl which had been boiled for 5 min and filled to set
as gel at room temperature at the end of the disposable glass
dropper. An internal solution was 3 M KCl and the spiral shape of
stainless steel wire (0.5 mm diameter) was dipped in the 3 M KCl
solution. It was connected to the constant current source as shown
in Fig. 1.
The constant current source was fabricated in-house by using 3-
terminal adjustable voltage regulator, LM317 (ST microelectronics,
Singapore). The operating current was designed in the range of 15–